1. Field of the Invention
The invention relates to heat exchangers.
2. Brief Description of the Prior Art
Coiled tube heat exchangers are widely used in the chemical and other industries to heat or cool fluids.
There has been a demand for high performance from coiled tube heat exchangers and this has resulted in very close packing of the tubing. An example of this is the "Minicoil" (Trade Mark) which is a planar coil unit of plastics tubing which may be packed face to face with other units in a suitable container. Each unit has separate inlet and outlet tube endings capable of connection to suitable manifolding, so that the coils are operable in parallel, and thence to a suitable heat exchange fluid circulation system. A further example of a heat exchanger utilising separate planar coil units of plastics tubing packed face to face is described in British Pat. No. 2017895. This heat exchanger is distinguished by having couplings for heat exchange fluid mounted on one side of the frame of the individual coil units. Due to the flexible nature of the plastics tubing both these heat exchangers employ extensive supporting frameworks for the individual planar coils or coil units.
Heat exchangers of the above described type have non-ideal heat exchange characteristics. The flow of process fluid is transverse to the plane of the coils. It is seen that the coils alter in temperature radially as the heat exchange fluid progresses through the coil. Also successive planar coils have the same inlet and outlet temperatures but as the flow of process fluid to be subjected to heat exchange, hereafter called "process fluid", progresses from coil to coil its temperature progressively approaches the temperature of the coil it is in contact with, particularly the outlet end of that coil, so that the heat exchange efficiency of successive planar coils decreases.
Heat exchangers comprising a plurality of coils of metal tubing, the coils being operative in parallel, wherein the coils are of cylindrical conformation and of differing diameters each coil being mounted co-axially about the coil of next smaller diameter, are also known.
Such heat exchangers, in use, greatly reduce variations in heat exchange efficiency. The coils of such heat exchangers, being of metallic construction, pose relatively simple support problems because of their rigidity.